This invention relates generally to rheology-modified thermoplastic elastomer (TPE) compositions that comprise an elastomeric ethylene/alpha (xcex1)-olefin (EAO) polymer or EAO polymer blend and a high melting propylene polymer, preparation of the compositions, use of such compositions in processes such as profile extrusion and injection molding to make articles of manufacture and the resulting articles of manufacture. This invention particularly relates to such compositions wherein both components are peroxide-modified, methods for preparing the compositions, such as by peroxide modifying a physical blend of the components, and use of such compositions to produce fabricated articles, some of which are thin-walled parts such as work boot shafts via injection molding, refrigerator gaskets via profile extrusion and automotive skins via sheet extrusion and or calendering and then thermoforming.
Manufacturers of elastomeric parts engage in an ongoing search for elastomers with processing characteristics that allow them to attain any or all of higher rates of productivity, improved quality and broader markets. Conventional processes used to make such parts include, without limitation, injection molding, profile extrusion, film extrusion, calendering, thermoforming, blown film, sheet extrusion processes. Four useful measures of how a formulation or composition will process are: shear thinning index (STI), melt strength: (MS), solidification temperature (ST) and upper service temperature (UST). Improvements in these properties have,a direct affect upon productivity, quality and market breadth relative to such elastomeric parts.
STI, as used herein, is a ratio of polymer viscosity at a specified low shear rate divided by polymer viscosity at a specified high shear rate. For ethylene/alpha-olefin (EAO) polymers, a conventional STI test temperature is 190xc2x0 centigrade (xc2x0 C). Polymer viscosity is conveniently measured in poise (dyne-second/square centimeter (cm2)) at shear rates within a range of from 0.1 radian per second (rad/sec) to 100 rad/sec and at 190xc2x0 C. under a nitrogen atmosphere using a dynamic mechanical spectrometer such as an RMS-800 or ARES from Rheometrics.
MS, as used herein, is a maximum tensile force, in centiNewtons (cN), measured on a molten filament of a polymer melt extruded from a capillary rheometer die at a constant shear rate of 33 reciprocal seconds (secxe2x88x921) while the filament is being stretched by a pair of nip rollers that are accelerating the filament at a rate of 0.24 centimeters per second per second (cm/sec2) from an initial speed of 1 cm/sec. The molten filament is preferably generated by heating 10 grams (g) of a polymer that is packed into a barrel of an Instron capillary rheometer, equilibrating the polymer at 190xc2x0 C. for five minutes (min) and then extruding the polymer at a piston speed of 2.54 cm/min through a capillary die with a diameter of 0.21 cm and a length of 4.19 cm. The tensile force is preferably measured with a Goettfert Rheotens that is located so that the nip rollers are 10 cm directly below a point at which the filament exits the capillary die.
ST, as used herein, is the temperature of the highest temperature peak endotherm measured during cooling (in xc2x0 C) with a differential scanning calorimeter (DSC), such as that sold by TA Instruments, Inc., as the polymer is first heated at a rate of 10xc2x0 C./minute (min) from ambient temperature to a temperature of 200xc2x0 C., then cooled at a rate of 10xc2x0 C./min to a temperature of xe2x88x9230xc2x0 C. and then typically reheated at a rate of 10xc2x0 C./min to a temperature of 200xc2x0 C.
UST, as used herein, is that temperature (xc2x0 C) at which a thermomechanical analyzer (TMA) penetration probe penetrates a specimen having a thickness of two to three millimeters (mm) to a depth of 900 micrometers (xcexcm). A suitable TMA is produced by TA Instruments, Inc. A one Newton (N) force is applied to the penetration probe as it rests on a surface of the specimen that is in a chamber where temperature is ramped at a rate of 5xc2x0 C./min.
When using a profile extrusion process, a manufacturer usually desires an elastomer that xe2x80x9cshear thinsxe2x80x9d or decreases in viscosity with applied shear forces. Because pressure drop across an extruder die and amperage required to turn an extruder screw are directly related to elastomer viscosity, a reduction in elastomer viscosity due to shear thinning necessarily leads to a lower pressure drop and a lower amperage requirement. The manufacturer can then increase extruder screw speed until reaching a limit imposed by amperage or pressure drop. The increased screw speed translates to an increase in extruder output. An increase in shear thinning also delays onset of surface melt fracture (OSMF), a phenomenon that otherwise limits extruder output. Surface melt fracture is usually considered a quality defect and manufacturers typically limit extruder output and suffer a productivity loss to reach a rate of production that substantially eliminates surface melt fracture.
When producing profile extrusions with thin walls and a complex geometry, a manufacturer looks for an elastomer with high MS and rapid solidification upon cooling in addition to good shear thinning behavior. A combination of a high MS and rapid solidification upon cooling (high ST) allows a part to be extruded hot and cooled below the elastomer""s solidification temperature before gravity and extrusion forces lead to shape distortion. Ultimately, for broad market acceptance, a finished part should also retain its shape despite short term exposure to an elevated temperature during processing, shipping or eventual use.
The characteristics of high STI, high MS, rapid solidification (high ST) and increased UST are also important to manufacturers who produce elastomeric parts via injection molding. Resin pressure during injection is directly related to viscosity of the resin under specific shear conditions. A viscosity reduction due to shear thinning lowers resin pressure and reduces clamp tonnage requirements. A high MS helps eliminate part distortion during removal of a non-molten, freshly molded part from a mold. In addition, rapid solidification and increased UST allow a second polymer to be injection molded over the part without that part being deformed or melted during the second injection. Rapid solidification leads to shorter cycle times. Finally, a part must retain its strength at service temperatures and an increase in UST opens up additional markets for elastomeric parts.
Elastomeric part manufacturers who fabricate thin-walled (e.g. 2.5 mm thick), injection molded parts such as shafts (with a height of, for example, 18 inches: (45.7 cm) for industrial work boots have additional requirements beyond those specified for injection molding. They require a Shore A hardness of 30-60, preferably 35-50, for comfort around a wearer""s calf. For articles of manufacture like work boots, they also seek a lower density material to make the resulting article lighter, good low temperature flexibility and improved resistance to chemicals, solvents or both. As an illustration, flexible polyvinylchloride (PVC) has a density of about 1.33 g per cubic centimeter (g/cc) and less than desirable cold temperature flexibility. Oil extended styrene block polymers such as styrene/butadiene/styrene (SBS) polymers have a density of about 1.05 g/cc and undesirable chemical resistance, solvent resistance or both.
Manufacturers who prepare elastomeric extruded and blown films and calendered sheets seek the same characteristics as those who use injection molding. An improved or increased shear thinning rheology leads to higher production rates before OSMF with its attendant variability in film or sheet thickness. A high MS promotes bubble stability in a blown film operation and provides a wide window of operations for further processing of such films via thermoforming. A high MS also promotes roll release during calendering. Rapid solidification or solidification at a higher temperature keeps an embossed calendering profile from collapsing or being wiped out. As with injection molding, an increase in UST leads to an expansion of potential markets for resulting film and sheets.
Linear EAO polymers produced via metallocene catalysis and substantially linear ethylene and EAO polymers (SLEPs) produced via constrained geometry catalysis have densities of 0.91 g/cc or less. These polymers provide additional options for fabricators of elastomeric parts. At least some of these polymers process like traditional thermoplastic polymers but have a degree of pliancy and flexibility typically associated with softer, rubberlike materials. With technology advances, certain of these polymers now have densities as low as about 0.86 g/cc and a Shore A hardness, measured in accordance with American Society of Testing and Materials (ASTM) test D-2240, of about 64. The latter polymers have excellent light and oxidation resistance, but their melting points may be as low as about 43xc2x0 C. due to their low levels of crystallinity.
The use of linear EAOs and SLEPs, particularly those with the lowest densities, has led to a desire for improvements in an overall balance of processing characteristics. The desire includes simultaneous advances in STI, MS, ST and UST. These advances are constrained by a requirement to substantially avoid generation of gel particles. Gel particles, when present, adversely affect the appearance of thin-walled extrusions, films and sheets.
U. S. patent application Ser. No. 60/012873, filed Mar. 5, 1996, teaches rheological modification of EAO copolymers via use of a peroxide. One benefit resulting from such use is an ability to increase the STI from 7.6 for an unmodified resin up to 158.5 for a modified resin. Use of a peroxide also yields an increase in melt strength at 150xc2x0 C. from 0.81 cN for unmodified resin to 66.75 cN for a modified resin. These benefits are achieved without a measurable gel content. Peroxide modification does not, however, result in any improvement in either UST or ST of an EAO copolymer.
W. K Fischer provides a variety of teachings regarding blends of an EAO polymer with a polyolefin. For example, U.S. Pat. No. 3,758,643 and U.S. Pat. No. 3,806,558 contain teachings about partially cured blends of an EAO copolymer with a polyolefin. U.S. Pat. No. 3,862,106 relates to thermoplastic dynamically cured blend of EAO copolymers with a polyolefin. Both partial curing and dynamic curing lead to an increase in insoluble gel content. Testing for insoluble gel content (or gel value) uses cyclohexane at 23xc2x0 C. An acceptable substitute is boiling xylene, a common solvent that yields a gel value 30-50% lower than that found using cyclohexane. Fischer provides several examples in which gel particles are present at a high enough level to cause unacceptable roughness when partially cured or dynamically cured compositions are extruded as a one eighth inch rod.
G. Von Bodungen et al. teach, in U.S. Pat. No. 3,957,919, incorporation of polyethylene (PE) into the thermodynamically cured EAO/polyolefin blend compositions of U.S. Pat. No. 3,862,106. The PE helps protect polyolefins such as polypropylene (PP) from chain scission. This leads, in turn, to an increased gel content as measured with cyclohexane.
A. Y. Coran et al. teach, in U.S. Pat. No. 4,130,535, thermoplastic vulcanizates (TPVs) comprising blends of a crystalline thermoplastic polyolefin and a vulcanized EAO copolymer rubber. These compositions have a high gel content as no more than about 3% of the rubber is extractable in cyclohexane at 23 C.
It has now surprisingly been found that even though rheology modification, such as by addition of a peroxide, has no effect on the ST or UST limit of an EAO polymer, it has a dramatic effect on the ST and UST limits of blends of at least one elastomeric EAO polymer or EAO polymer blend and a high melting polyolefin such as PP. In addition, rheology modification of such blends yields a STI that exceeds the STI of (a) a rheology modified EAO polymer or EAO polymer blend or (b) a blend, without rheology modification, of the same high melting polyolefin and an EAO polymer or EAO polymer blend. As such, one aspect of this invention is a rheology-modified, substantially gel-free thermoplastic elastomer (TPE) composition comprising an EAO polymer or EAO polymer blend and at least one high melting polymer selected from the group consisting of polypropylene homopolymers and propylene/ethylene copolymers, the composition having a combination of at least three of four characteristics, the characteristics being a shear thinning index of at least 20, a melt strength that is at least (xe2x89xa7) 1.5 times that of the composition without rheology modification, a solidification temperature that is at least 10xc2x0 C. greater than that of the composition without rheology modification, and an upper service temperature limit that is at least 10xc2x0 C. greater than that of the composition without rheology modification.
The rheology-modified ITE compositions may be compounded with conventional additives or process aids including, for example, fillers, stabilizers, dispersants, pigments and process oils. Compounds prepared from the rheology modified polymers of this invention retain their processing advantages over compounds prepared from the same polymers, but without rheology modification. The rheology modification is preferably induced via a peroxide, but may be accomplished thermally or by irradiation, including e-beam.
In a first related aspect, the TPE compositions of the first aspect may further comprise at least one additive selected from the group consisting of process oils, fillers and blowing agents.
In a second related aspect, the TPE compositions of the first aspect may be blended with another polymer, preferably one of the polymers used to make the TPE composition, prior to fabrication of an article of manufacture. Such blending may occur by any of a variety of conventional techniques, one of which is dry blending of pellets of the TPE composition with pellets of another polymer.
A second aspect of this invention is a process for preparing a rheology-modified, substantially gel-free TPE composition, the process comprising: a) providing a combination of an organic peroxide and a molten polymer composition that comprises at least one of (1) an elastomeric ethylene/alpha-olefin polymer or ethylene/alpha-olefin polymer blend and (2) a high melting polymer selected from the group consisting of polypropylene homopolymers and propylene/ethylene copolymers; and b) maintaining the combination in a melt state while subjecting it to conditions of shear sufficient to disperse the peroxide throughout the molten polymer composition, effect sufficient rheology modification of the molten polymer composition and substantially preclude formation of insoluble polymer gels, sufficient rheology modification being measured by a combination of at least three of four characteristics, the characteristics being a shear thinning index of at least 20, a melt strength that is at least about 1.5 times that of the polymer blend without rheology modification, a solidification temperature that is at least 10xc2x0 C. greater than that of the polymer blend without rheology modification, and an upper service temperature limit that is at least 10xc2x0 C. greater than that of the polymer blend without rheology modification. The process optionally includes a step c) wherein the rheology modified polymer blend is converted to an article of manufacture that has the combination of at least three of four characteristics. If the process includes step c), it may be further modified to comprise sequential intermediate steps b1) and b2) that precede step c), step b1) comprising recovery of the rheology modified polymer blend as a solid and step b2) comprising conversion of the solid to a melt state sufficient for fabricating the article of manufacture.
One variation of the second aspect involves adding the high melting polymer to the molten polymer composition while the composition is in a melt state, but subsequent to rheology modification of the elastomeric ethylene/alpha-olefin polymer or elastomeric ethylene/alpha-olefin polymer blend.
A second variation of the second aspect involves adding, either before or after step b), at least one additive selected from the group consisting of process oils, fillers and blowing agents, the process oil being present in an amount within a range of from 0 to about 50 weight percent, the filler being present in an amount within a range of from 0 to about 70 weight percent, and the blowing agent being present in an amount within a range of from 0 to about 10 weight percent, all amounts being based on total composition weight, the filler, when present, being selected from the group consisting of glass, silica, carbon black, metal carbonates, metal sulfates, talc, clay and graphite fibers.
A third aspect of this invention is an article of manufacture having at least one component thereof fabricated from the TPE composition of the first aspect of the invention or prepared by the process of the second aspect of the invention. The compositions readily allow formation of articles of manufacture using apparatus with suitable upper pressure limitations combined with relatively long flow paths and narrow flow channels. The following paragraph contains a partial listing of suitable articles of manufacture.
The compositions of this invention can be formed into a variety of shaped articles using conventional polymer fabrication processes such as those identified above. A partial, far from exhaustive, listing of suitable shaped articles includes automobile body parts such as bumper fascia, body side moldings, exterior trim, interior trim, air dams, air ducts, wheel covers and instrument and door panel skins, and non-automotive applications such as polymer films, polymer sheets, trash cans, storage containers, swim fins, lawn furniture strips or webbing, lawn mower and other garden appliance parts, recreational vehicle parts, golf cart parts, utility cart parts and water craft parts. The compositions can also be used in roofing applications such as roofing membranes. The compositions can further be used in fabricating components of footwear such as a shaft for a boot, particularly an industrial work boot. A skilled artisan can readily augment this list without undue experimentation.
The rheology-modified compositions of this invention comprise an elastomeric EAO polymer or EAO polymer blend and a high melting polymer. The compositions desirably contain the EAO polymer or EAO polymer blend in an amount of from about 50 to about 90 wt % and the high melting polymer(s) in an amount of from about 50 to about 10 wt %, both percentages being based on composition weight. The amounts are preferably from about 65 to about 85 wt % EAO and from about 35 to about 15 wt % high melting polymer. The amounts are chosen to total 100 wt %.
EAO polymers (also referred to as xe2x80x9cethylene polymersxe2x80x9d) that are suitable for this invention include interpolymers and diene modified interpolymers. Illustrative polymers include ethylene/propylene (EP) copolymers, ethylene/butylene (EB) copolymers, ethylene/octene (EO) copolymers, ethylene/alpha-olefin/diene modified (EAODM) interpolymers and ethylene/propylene/diene modified (EPDM) interpolymers. More specific examples include ultra low linear density polyethylene (ULDPE) (e.g., Attane(trademark) made by The Dow Chemical Company), homogeneously branched, linear EAO copolymers (e.g. Tafmer(trademark) by Mitsui PetroChemicals Company Limited and Exact(trademark) by Exxon Chemical Company), and homogeneously branched, substantially linear EAO polymers (e.g. the Affinity(trademark) polymers available from The Dow Chemical Company and Engage(copyright) polymers available from DuPont Dow Elastomers L.L.C. The more preferred EAO polymers are the homogeneously branched linear and substantially linear ethylene copolymers with a density (measured in accordance with ASTM D-792) of from about 0.85 to about 0.92 g/cc, especially from about 0.85 to about 0.90 g/cc and a melt index or 12 (measured in accordance with ASTM D-1238 (190xc2x0 C./2.16 kg weight) of from about 0.01 to about 30, preferably 0.05 to 10 g/10 min.
The substantially linear ethylene copolymers or interpolymers (also known as xe2x80x9cSLEPsxe2x80x9d) are especially preferred. In addition, the various functionalized ethylene copolymers such as EVA (containing from about 0.5 to about 50 wt % units derived from vinyl acetate) are also suitable. When using an EVA polymer, those that have an 12 of from about 0.01 to about 500, preferably 0.05 to 50 g/10 min are preferred.
xe2x80x9cSubstantially linearxe2x80x9d means that a polymer has a backbone substituted with from 0.01 to 3 long-chain branches per 1000 carbons in the backbone.
xe2x80x9cLong-chain branchingxe2x80x9d or xe2x80x9cLCBxe2x80x9d means a chain length that exceeds that of a short chain that results from incorporation of an alpha-olefin into the backbone of an EAO polymer or an EAO polymer blend. Although carbon-13 nuclear magnetic resonance (C13 NMR) spectroscopy cannot distinguish or determine an actual number of carbon atoms in the chain if the length is greater than six carbon atoms, the presence of LCB can be determined, or at least estimated, from molecular weight distribution (MWD) of the EAO polymer(s). It can also be determined from a melt flow ratio (MFR) or ratio (I10/I2) of melt index (I10), determined via ASTM D-1238 (190xc2x0 C., 10 kg weight) to I2.
xe2x80x9cInterpolymerxe2x80x9d refers to a polymer having polymerized therein at least two monomers. It includes, for example, copolymers, terpolymers and tetrapolymers. It particularly includes a polymer prepared by polymerizing ethylene with at least one comonomer, typically an alpha olefin (xcex1-olefin) of 3 to 20 carbon atoms (C3-C20). Illustrative xcex1-olefins include propylene, 1-butene, 1-hexene, 4-methyl-1-pentene, 1-heptene, 1-octene and styrene. The xcex1-olefin is desirably a C3-C10 xcex1-olefin. Preferred copolymers include EP, EB, ethylene/hexene-1 (EH) and EO polymers. Illustrative terpolymers include an ethylene/propylene/octene terpolymer as well as terpolymers of ethylene, a C3-C20 xcex1-olefin and a diene such as dicyclopentadiene, 1,4-hexadiene, piperylene or 5-ethylidene-2-norbornene.
xe2x80x9cElastomericxe2x80x9d, as used herein, means an EAO polymer or EAO polymer blend that has a density that is beneficially less than about 0.910 g/cc, desirably less than about 0.900 g/cc, preferably less than about 0.895 g/cc, more preferably less than about 0.880 g/cc, still more preferably less than about 0.875 g/cc, even more preferably less than about 0.870 g/cc and a percent crystallinity of less than about 33%, preferably less than about 29% and more preferably less than about 23%. The density is preferably greater than about 0.850 g/cc. Percent crystallinity is determined by differential scanning calorimetry (DSC)
SLEPs are characterized by narrow MWD and narrow short chain branching distribution (SCBD) and may be prepared as described in U.S. Pat. Nos. 5,272,236 and 5,278,272, relevant portions of both being incorporated herein by reference. The SLEPs exhibit outstanding physical properties by virtue of their narrow MWD and narrow SCBD coupled with long chain branching (LCB).
U.S. Pat. No. 5,272,236 (column 5, line 67 through column 6, line 28) describes SLEP production via a continuous controlled polymerization process using at least one reactor, but allows for multiple reactors, at a polymerization temperature and pressure sufficient to produce a SLEP having desired properties. Polymerization preferably occurs via a solution polymerization process at a temperature of from 20xc2x0 C. to 250xc2x0 C., using constrained geometry catalyst technology. Suitable constrained geometry catalysts are disclosed at column 6, line 29 through column 13, line 50 of U.S. Pat. No. 5,272,236.
A preferred SLEP has a number of distinct characteristics, one of which is an ethylene content that is between 20 and 90 wt %, more preferably between 30 and 89 wt %, with the balance comprising one or more comonomers. The ethylene and comonomer contents are based on SLEP weight and selected to attain a total monomer content of 100 wt %. For chain lengths up to six carbon atoms, SLEP comonomer content can be measured using C13 NMR spectroscopy.
Additional distinct SLEP characteristics include I2 and MFR or I10/I2. The interpolymers desirably have an I2 of 0.01-30 g/10 min, more preferably from 0.05-10 g/10 min. The SLEP also has a I10/I2 (ASTM D-1238)xe2x89xa75.63, preferably from 6.5 to 15, more preferably from 7 to 10. For a SLEP, the I10/I2 ratio serves as an indication of the degree of LCB such that a larger I10/I2 ratio equates to a higher degree of LCB in the polymer.
SLEPs that meet the aforementioned criteria include, for example, ENGAGE(copyright) polyolefin elastomers and other polymers produced via constrained geometry catalysis by The Dow Chemical Company and DuPont Dow Elastomers L.L.C.
The high melting polymer (polyolefin) component of the TPEs of this invention is a homopolymer of propylene or a copolymer of propylene with an (xcex1-olefin such as ethylene, 1-butene, 1-hexene or 4-methyl-1-pentene or a blend of a homopolymer and a copolymer or a nucleated homopolymer, a nucleated copolymer or a nucleated blend of a homopolymer and a copolymer. The xcex1-olefin is preferably ethylene. The copolymer may be a random copolymer or a block copolymer or a blend of a random copolymer and a block copolymer. As such, this component is preferably selected from the group consisting of polypropylene (PP) homopolymers and propylene/ethylene copolymers. This component has a melt flow rate (MFR) (230xc2x0 C. and 2.16 kg weight) of 0.3 to 60 g/10 min, preferably 0.8 to 40 g/10 min and more preferably 1 to 35 g/10 min.
As used herein, xe2x80x9cnucleatedxe2x80x9d refers to a polymer that has been modified by addition of a nucleating agent such as Millad(trademark), a dibenzyl sorbitol commercially available from Milliken. Other conventional nucleating agents may also be used.
Preparation of polypropylene (PP) also involves the use of Ziegler catalysts such as a titanium trichloride in combination with aluminum diethylmonochloride, as described by Cecchin, U.S. Pat. No. 4,177,160. Polymerization processes used to produce PP include the slurry process, which is run at about 50-90xc2x0 C. and 0.5-1.5 MPa (5-15 atm), and both the gas-phase and liquid-monomer processes in which extra care must be given to the removal of amorphous polymer. Ethylene may be added to the reaction to form a polypropylene with ethylene blocks. PP resins may also be prepared by using any of a variety of metallocene, single site and constrained geometry catalysts together with their associated processes.
Suitable organic peroxides have a half life of at least one hour at 120xc2x0 C. Illustrative peroxides include a series of vulcanizing and polymerization agents that contain xcex1, xcex1xe2x80x2-bis(t-butylperoxy)-diisopropylbenzene and are available from Hercules, Inc. under the trade designation VULCUP(trademark), a series of such agents that contain dicumyl peroxide and are available from Hercules, Inc. under the trade designation Di-cup(trademark) as well as Lupersol(trademark) peroxides made by Elf Atochem, North America or Trigonox(trademark) organic peroxides made by Moury Chemical Company. The Lupersol(trademark) peroxides include Lupersol(trademark) 101 (2,5-dimethyl-2,5-di(t-butylperoxy)hexane), Lupersol(trademark) 130 (2,5-dimethyl-2,5-di(t-butylperoxy)hexane-3) and Lupersol(trademark) 575 (t-amylperoxy-2-ethylhexonate). Other suitable peroxides include 2,5-dimethyl-2,5-di-(t-butylperoxy)hexane, di-t-butylperoxide, 2,5-di(t-amylperoxy)-2,5-dimethylhexane, 2,5-di-(t-butylperoxy)-2,5-diphenylhexane, bis(alpha-methylbenzyl)peroxide, benzoyl peroxide, t-butyl perbenzoate and bis(t-butylperoxy)-diisopropylbenzene.
The peroxide is used in an amount sufficient to provide at least three of the following four characteristics: a STI of at least 20, preferably at least 25, more preferably at least 30 and still more preferably at least 35, a MS that is at least 1.5 times, preferably at least 1.6 times and more preferably at least two times that of the composition without rheology modification, a ST that is at least 10xc2x0 C. greater than that of the composition without rheology modification, and an UST limit that is at least 10xc2x0 C. greater than that of the composition without rheology modification. The peroxide is suitably present in an amount that is within a range of from about 1500 to about 10,000 parts by weight per million parts by weight of polymer (ppm). The range is desirably from about 2,000 to about 8,000, preferably from about 3,000 to about 6,000 ppm.
The peroxide can be added by any conventional means known to skilled artisans. If a processing oil is to be used in preparing the rheology-modified compositions of the invention, the peroxide may be injected during processing, as a solution or dispersion in the processing oil or another dispersing aid, into a processing apparatus at a point where the polymer blend is in a melt state. Concentration of the peroxide in the solution or dispersion may vary, but a 20 to 40 percent by weight (wt %) concentration, based on solution or dispersion weight, provides acceptable results. The solution or dispersion can also be admixed with and allowed to imbibe on dry blended polymer pellets. If the peroxide is a liquid, it may be used as; is without forming a solution or dispersion in a processing oil. One can, for example, add a liquid peroxide to a high speed blender together with dry polymer pellets, subject the blender contents to mixing action for a short period of time and then allow the contents to rest until imbibing action is regarded as sufficiently complete. On a small scale, a Welex Papenmeier Type TGAHK20 blender (Papenmeier Corporation) can be used to provide: mixing action for a time period such as 30-45 seconds. This is typically followed by a rest period of about 30 minutes. A more preferred procedure involves introducing the peroxide as a solid into the compounding apparatus together with the polymer pellets as the pellets enter a compounding apparatus such as at the throat of an extruder, adding it to a polymer melt in a compounding apparatus such as a Haake, a Banbury mixer, a Farrel continuous mixer or a Buss kneader. Alternately, the peroxide can be added as a solid in conjunction with dry blending of the polymer pellets.
In order to detect the presence of, and where desirable, quantify insoluble gels in a polymer composition such as the rheology-modified compositions of this invention, simply soak the composition in a suitable solvent such as refluxing xylene for 12 hours as described in ASTM D 2765-90, method B. Any insoluble portion of the composition is then isolated, dried and weighed, making suitable corrections based upon knowledge of the composition. For example, the weight of non-polymeric components that are soluble in the solvent is subtracted from the initial weight and the weight of non-polymeric components that are insoluble in the solvent is subtracted from both the initial and final weight. The insoluble polymer recovered is reported as percent gel (% gel) content. For purposes of this invention, xe2x80x9csubstantially gel-freexe2x80x9d means a percent gel content that is desirably less than about 10%, more desirably less than about 8%, preferably less than about 5%, more preferably less than about 3%, still more preferably less than about 2%, even more preferably less than about 0.5% and most preferably below detectable limits when using xylene as the solvent. For certain end use applications where gels can be tolerated, the percent gel content can be higher.
The compositions of this invention may be compounded with any one or more materials conventionally added to polymers. These materials include, for example, EAOs that have not been rheology modified, process oils, plasticizers, specialty additives including stabilizers, fillers (both reinforcing and non-reinforcing) and pigments. These materials may be compounded with compositions of this invention either before or after such compositions are rheology modified. Skilled artisans can readily select any suitable combination of additives and additive amounts as well as timing of compounding without undue experimentation.
If the rheology-modified EAO polymer blend is further modified or admixed with an EAO that has not been rheology-modified, such as an EO copolymer, with a Mooney viscosity (ML1+4, 125xc2x0 C.)xe2x89xa720, desirablyxe2x89xa740, preferablyxe2x89xa750, more preferablyxe2x89xa760 and still more preferablyxe2x89xa770, the unmodified EAO is desirably present in an amount that falls within a range of from greater than 0 to 30 wt %, based on total composition weight. The range is preferably from 5 to 20 wt %, more preferably from 8 to 20 wt %.
Process oils are often used to reduce any one or more of viscosity, hardness, modulus and cost of a composition. The most common process oils have particular ASTM designations depending upon whether they are classified as paraffinic, naphthenic or aromatic oils. An artisan skilled in the processing of elastomers in general and the rheology-modified TPE compositions of this invention in particular will recognize which type of oil will be most beneficial. The process oils, when used, are desirably present in an amount within a range of from about 15 to about 50 wt %, based on total composition weight.
A variety of specialty additives may be advantageously used in compositions of this invention. The additives include antioxidants, surface tension modifiers, anti-block agents, lubricants, antimicrobial agents such as organometallics, isothtazolones, organosulfurs and mercaptans; antioxidants such as phenolics, secondary amines, phophites and thioesters; antistatic agents such as quaternary ammonium compounds, amines, and ethoxylated, propoxylated or glycerol compounds; fillers and reinforcing agents such as carbon black, glass, metal carbonates such as calcium carbonate, metal sulfates such as calcium sulfate, talc, clay or graphite fibers; hydrolytic stabilizers; lubricants such as fatty acids, fatty alcohols, esters, fatty amides, metallic stearates, paraffinic and microcrystalline waxes, silicones and orthophosphoric acid esters; mold release agents such as fine-particle or powdered solids, soaps, waxes, silicones, polyglycols and complex esters such as trimethylolpropane tristearate or pentaerythritol tetrastearate; pigments, dyes and colorants; plasticizers such as esters of dibasic acids (or their anhydrides) with monohydric alcohols such as o-phthalates, adipates and benzoates; heat stabilizers such as organotin mercaptides, an octyl ester of thioglycolic acid and a barium or cadmium carboxylate; ultraviolet light stabilizers used as a hindered amine, an o-hydroxy-phenylbenzotriazole, a 2-hydroxy, 4-alkoxyenzophenone, a salicylate, a cynoacrylate, a nickel chelate and a benzylidene malonate and oxalanilide; and zeolites, molecular sieves and other known deodorizers. A preferred hindered phenolic antioxidant is Irganox(trademark) 1076 antioxidant, available from Ciba-Geigy Corp. Each of the above additives, if used, typically does not exceed 45 wt %, based on total composition weight, and are advantageously from about 0.001 to about 20 wt %, preferably from about 0.01 to about 15 wt % and more preferably from about 0.1 to about 10 wt %.
The rheology-modified TPE compositions of this invention may be fabricated into parts, sheets or other form using any one of a number of conventional procedures for processing TPEs. The compositions can also be formed, spun or drawn into films, fibers, multi-layer laminates or extruded sheets, or can be compounded with one or more organic or inorganic substances, on any machine suitable for such purposes.
The TPE compositions: of this invention have surprisingly improved properties relative to simple blends of an EAO copolymer and a high melting polymer such as PP that have not been subjected to rheology modification. Rheology modification, whether it be by way of an organic peroxide or other free radical generating compound, use of a source of radiation, such as ultraviolet light or e-beam, or application of heat, with or without a compound such as an organic peroxide, provides a combination of at least three of four desirable and improved properties. Two of the properties of interest are an STI of at least 20, preferably at least 25, more preferably at least 30 and still more preferably at least 35, and an UST limit, as measured by Rheometrics Dynamic Analysis (RDA), that is at least 10xc2x0 C. greater than that of the composition without rheology modification. In an uncompounded state, two additional properties of interest for compositions of the present invention are a MS that is at least 1.5, preferably at least 1.6 and more preferably at least 2 times that of a like composition save for the absence of the rheology modification, and a ST that is at least 10xc2x0 C. greater than that of the composition without rheology modification.